This proposal seeks to understand how regulatory genes control CNS development. Specifically, it explores the regulation and function of the single-minded gene, which controls the formation of a group of neurons and glia that lie along the midline of the Drosophila CNS. Genes that control dorsal-ventral patterning activate single-minded transcription specifically in the midline precursor cells. single-minded then activates transcription of a large group of genes that carry-out the CNS midline lineage developmental program. Sequence analysis indicates that single-minded belongs to the basic-helix-loop-helix family of transcription factors, which includes regulators of nervous system and muscle development as well as growth control, carcinogen metabolism, and sex determination. In this grant, we will investigate how single-minded controls midline gene expression at the biochemical level. Additionally, the role of genes shown by genetics to influence single-minded transcription will be investigated using biochemistry and germline transformation.